The invention relates generally to a copying method and apparatus.
More particularly, the invention relates to a copying method and apparatus in which the an original, especially a colored original, is scanned to generate imaging signals which are then processed to improve the quality of an image of the original.
In a known procedure for copying an original, the original is scanned along rows and columns, or point-by-point, to generate a set of imaging signals which represent an image of the original. The signals are processed in order to ensure that the tones of the image properly reflect those of the original. The processed signals are sent to a cathode ray tube which prints the image on color copy material by rows and columns or point-by-point. Signals may also undergo processing to adjust exposure parameters of the image such as gray balance and contrast. The processed signals are sent to a cathode ray tube which prints the image on color copy material by rows and columns or point-by-point.
Electronic image processing is being increasingly used in the reproduction of colored originals (positive-positive) and the production of colored photographic positives from color negatives. See, for example, the European Patent Application Nos. 123 701 and 168 818. Here, the original to be copied is electrooptically scanned along rows and columns, or point-by-point, and the resulting imaging signals are modified in accordance with specific criteria. As a rule, the imaging signals defining the image of the original are digitized, and the imaging signals may then be stored in digital memories. Scanning of the original is normally performed serially in the three primary colors red, green and blue (RGB).
The imaging signals are converted into optical images on copy material using printers with cathode ray tubes, also known as CRT printers. See, for instance, Journal of Imaging Technology, 12, No. 3 (June 1986), pp. 135-139. A problem with such apparatus is that the image processing operation generates imaging signals which are optimized in a specific manner, as regards color reproduction and contrast or sharpness, for the electronic reproduction of the image. In order that such signals may yield a properly colored copy having proper contrast when used to expose a color copy material via a cathode ray tube, the characteristics of the color copy material in relation to sensitivity and gradation, as well as the characteristics of the cathode ray tube, must be correctly taken into account.
Adjustment of the imaging signals to the non-linear characteristic function or line of the cathode ray tube is accomplished by means of a suitable amplifier disposed immediately before the cathode ray tube so that the characteristic function of the tube does not affect the gray balance and contrast. The characteristic blackening or darkening functions of the copy material are likewise nonlinear. Due to this non-linearity, changes in the amounts of light for the purpose of gray compensation influence the contrast of the tube, and vice versa. This interaction of adjustments makes it difficult and tedious to achieve the proper settings for gray balance and contrast using test copies because an iteration process which, under favorable circumstances, reduces the magnitudes of errors, is required.